1. Field of the Invention
This invention concerns aqueous chemical mechanical polishing compositions and slurries that are useful for polishing substrates including metal features such as copper and tantalum features. The aqueous polishing compositions comprise a film-forming agent and at least one silane composition. In one method, the polishing compositions of this invention are used by applying the composition to an abrasive pad or by combining the composition with one or more abrasives to form a polishing slurry and then using the pad or slurry to polish a substrate including one or more metal features.
2. Description of the Art
Integrated circuits are made up of millions of active devices formed in or on a silicon substrate. The active devices, which are initially isolated from one another, are interconnected to form functional circuits and components. The devices are interconnected through the use of multilevel interconnections. Interconnection structures normally have a first layer of metallization, an interconnection layer, a second level of metallization, and sometimes a third and subsequent level of metallization. Interlevel dielectrics such as doped and undoped silicon dioxide (SiO2), or low-xcexa dielectrics tantalum nitride are used to electrically isolate the different levels of metallization in a silicon substrate or well. The electrical connections between different interconnection levels are made through the use of metallized vias. U.S. Pat. No. 5,741,626, which is incorporated herein by reference, describes a method for preparing dielectric tantalum nitride layers.
In a similar manner, metal contacts are used to form electrical connections between interconnection levels and devices formed in a well. The metal vias and contacts may be filled with various metals and alloys including titanium (Ti), titanium nitride (TiN), tantalum (Ta), aluminum copper (Alxe2x80x94Cu), aluminum silicon (Alxe2x80x94Si), copper (Cu), tungsten (W), and combinations thereof. The metal vias and contacts generally employ an adhesion layer such as titanium nitride (TiN), titanium (Ti), tantalum (Ta), tantalum nitride (TaN) or combinations thereof to adhere the metal layer to the SiO2 substrate. At the contact level, the adhesion layer acts as a diffusion barrier to prevent the filled metal and SiO2 from reacting.
In many semiconductor manufacturing processes, metallized vias or contacts are formed by a blanket metal deposition followed by a chemical mechanical polish (CMP) step. In a typical process, via holes are etched through an interlevel dielectric (ILD) to interconnection lines or to a semiconductor substrate. Next, a thin adhesion layer such as tantalum nitride and/or tantalum is generally formed over the ILD and is directed into the etched via hole. Then, a metal film is blanket deposited over the adhesion layer and into the via hole. Deposition is continued until the via hole is filled with the blanket deposited metal. Finally, the excess metal is removed by chemical mechanical polishing (CMP) to form metal vias. Processes for manufacturing and/or CMP of vias are disclosed in U.S. Pat. Nos. 4,671,851, 4,910,155 and 4,944,836.
In a typical chemical mechanical polishing process the substrate is placed in direct contact with a rotating polishing pad. A carrier applies pressure against the backside of the substrate. During the polishing process, the pad and table are rotated while a downward force is maintained against the substrate back. An abrasive and chemically reactive solution, commonly referred to as a xe2x80x9cslurryxe2x80x9d is applied to the pad during polishing. The slurry initiates the polishing process by chemically reacting with the film being polished. The polishing process is facilitated by the rotational movement of the pad relative to the substrate as slurry is provided to the wafer/pad interface. Polishing is continued in this manner until the desired film on the insulator is removed. Polishing composition formulation is an important factor in the CMP step. The polishing composition should be tailored to provide effective polishing to metal layers at desired polishing rates while minimizing surface imperfections, defects and corrosion and erosion. Furthermore, the polishing composition may be used to provide controlled polishing selectivities to other thin-film materials used in current integrated circuit technology such as titanium, titanium nitride, tantalum, tantalum nitride, and the like.
There are various mechanisms disclosed in the prior art by which metal surfaces can be polished with slurries. The metal surface may be polished using a slurry in which a surface film is not formed in which case the process proceeds by mechanical removal of metal particles and their dissolution in the slurry. In such a mechanism, the chemical dissolution rate should be slow in order to avoid wet etching. A more preferred mechanism is, however, one where a thin abradable layer is continuously formed by reaction between the metal surface and one or more components in the slurry such as a complexing agent and/or a film-forming layer. The thin abradable layer is then removed in a controlled manner by mechanical action. Once the mechanical polishing process has stopped, a thin passive film remains on the surface and controls the wet etching process. Controlling the chemical mechanical polishing process is much easier when a CMP slurry polishes using this mechanism.
Current copper containing substrates that are polished using chemical mechanical polishing also use Ta and TaN adhesion layers. Ta and TaN are chemically very passive and mechanically very hard and, consequently, difficult to remove by polishing. Thus, there remains a need for polishing compositions that are useful for polishing substrates including tantalum while having little detrimental effect on previously polished copper features.
In one embodiment, this invention includes aqueous chemical mechanical polishing compositions comprising a film-forming agent and at least one silane compound.
In another embodiment, this invention includes an aqueous chemical mechanical polishing composition comprising from about 0.01 to about 0.5 wt % benzotriazole and from about 0.05 to about 1.0 wt % uriedopropyltrimethoxysilane and, further, optionally including from about 1.0 to about 30 wt % silica abrasive.
In yet another embodiment, this invention is a method for polishing a substrate feature. The method includes moving a substrate including at least one feature into contact with a polishing pad. Next, the substrate is moved in relationship to the polishing pad to remove a portion of the substrate feature. A liquid polishing composition is applied to the polishing pad to promote polishing wherein the liquid polishing composition comprises at least one film-forming agent and at least 0.001 wt % of at least one silane compound.
The polishing compositions of the present invention have been found to be effective in polishing the metal features of an integrated circuit with few defects.